The present invention generally relates to a semiconductor processing furnace and more particularly, relates to an apparatus for holding a semiconductor processing furnace tube that is provided in a two-piece construction.
In connection with processes used to manufacture semiconductor devices, such as integrated circuits, numerous process steps are carried out in a controlled environment at elevated temperatures. Such processes includes oxidation, diffusion, chemical vapor deposition and annealing. In order to realize elevated processing temperatures, semiconductor wafers are processed in an evacuated chamber, typically in a form of a quartz tube which is housed within a semiconductor furnace.
The most common type of semiconductor furnace is of the so-called xe2x80x9chot wallxe2x80x9d electric type which facilitates batch processing of semiconductor wafers. Furthermore, hot wall electric furnaces exhibit excellent temperature stability and precise temperature control. Modern hot wall diffusion furnaces are capable of controlling temperatures over the range of 300xc2x0-1200xc2x0 C. to an accuracy of 0.5xc2x0 or xe2x88x920.5xc2x0 C. Hot wall furnaces were initially designed as horizontal diffusion furnaces, however, more recently, vertical furnaces have gained favor because they present a number of advantages over their horizontal predecessors. These advantages include: elimination of cantilever or soft-landing since the wafers are held in a quartz boat which does not touch the process tube walls; wafers can be loaded and unloaded automatically; and, the clean room footprint of the system is somewhat smaller than that of the conventional horizontal configuration.
FIGS. 1xcx9c3 illustrate a conventional semiconductor furnace, generally indicated by the numeral 10 employed to carry out processes used in manufacturing semiconductor devices, such as integrated circuits. The furnace 10 is of the so-called vertical type, having a cylindrical heating body 12 provided with a closed upper end, and a lower open end. The body 12 typically would include a plurality of electrical heating elements (not shown) therein coupled with a suitable power source for heating the interior cavity of the body 12 to a temperature of, for example, 180 to 250xc2x0 C. The lower end of the heater body 12 is provided with a flat metal base 16 having a circular opening in the middle thereon, coaxial with the longitudinal, central axis of the body 12. Either or both of the body 12 and base 16 may be provided with conduits (not shown) therein coupled with a source of cooling water for accelerating the cool down of the furnace, as may be required in certain manufacturing processes.
A processing chamber in the form of a quartz tube assembly generally indicated by the numeral 35 includes a fragile, quartz tube 14 having a generally cylindrically sidewall disposed within the furnace body 12, coaxial with the latter. The tube 14 secured on a base flange 18 by means of a reaction tube anchor ring 32 and cushion ring 34 which are sleeved over the tube 14 so as to engage a lip 37 on the lower end of the tube 14. A Teflon seal-ring 36 and O-ring 40 are sandwiched between the lip 37 and upper surface of the flange 18. The anchor ring 32 is drawn down against the flange 18 by suitable fasteners to create an air tight seal between the tube 14 and flange 18. The flange 18 includes the three circumferentially spaced mounting ears 22 provided with fasteners 24 that secure the base 18, and thus the tube assembly 35, on standoffs 25 that extend downwardly from the base 16. As best seen in FIG. 3, the anchor ring 32 may be provided with an internal, circumferentially extending fluid conduit coupled with inlets/outlets 39 which are in turn coupled with a source of cooling water in order to draw heat away from the tube assembly 35. The flange 18 also includes an inlet opening 20 which is adapted to be coupled with a vacuum pump (not shown) or gas supply for evacuating the tube and filling it with processing gases.
A semiconductor wafer boat elevator 41 includes a boat support 26 coupled by a lateral arm 28 to a vertical spiral drive 30 which moves the elevator up and down, beneath the furnace 12.
In order to remove or install the tube assembly 35 in the furnace body 12, the fasteners 24 are released and the boat elevator 41 is moved upwardly until the flange rests on the support 26. Motor means (not shown) is then activated to lower the boat elevator 41, whereupon the tube assembly 35 moves downwardly through the bottom opening of the furnace body 12.
Vertical semiconductor furnaces of the type mentioned above employ a quartz tube which typically has a polysilicon coating when used for a deposition or annealing process. The polysilicon deposition reduces the power loss due to quartz reflection or radiation, and reduces the degradation of a boat occasioned by wet etching. Because semiconductor furnaces are subjected to high rates of usage and their components are exposed to harsh operating environments, periodic maintenance must be performed on various furnace components, including the quartz tube assembly.
For instance, as shown in FIGS. 4 and 5, a periodic maintenance procedure is performed when the tube assembly 35 is positioned on a maintenance cart 50. When the anchor ring 32 is mounted onto the base 18 by a plurality of bolts 44, as shown in FIG. 4, the tube assembly 35 is positioned on the maintenance cart 50 and removed from the furnace 10. After the mounting bolts 44 are removed, the anchor ring 32 (also known as a quartz holder ring) and an aluminum gasket 52 must be removed from the quartz tube 14 in order to disassemble the tube assembly 35 for cleaning. In modern semiconductor process equipment, such as in a furnace for processing 300 mm wafers, the outer tube, or quartz tube 14 has a large diameter and length. It becomes a difficult task to remove the quartz holder ring 32 from the quartz tube 14 without accidentally touching the tube. When the quartz holder ring 32 touches the quartz tube 14 during the removal process, the touching can cause scratching of the tube surface and furthermore, generation of contaminating particles from the quartz holder ring 32.
It is therefore an object of the present invention to provide an apparatus for fixing the position of a furnace tube in a semiconductor processing furnace that does not have the drawbacks or shortcomings of the conventional apparatus.
It is another object of the present invention to provide an apparatus for fixing the position of a furnace tube in a semiconductor processing furnace that can be easily removed from the furnace tube.
It is a further object of the present invention to provide an apparatus for fixing the position of a furnace tube in a semiconductor processing furnace wherein the apparatus can be easily removed from the furnace tube without touching the tube surface.
It is another further object of the present invention to provide an apparatus for fixing the position of a furnace tube in a semiconductor processing furnace wherein the apparatus is provided sin two clamp halves for functioning as a quartz holder ring.
It is still another object of the present invention to provide an apparatus for fixing the position of a furnace tube in a semiconductor processing furnace wherein the apparatus is provided in a clam-shell configuration for easy removal from the tube surface.
In accordance with the present invention, an apparatus for holding a quartz furnace tube or an apparatus for fixing the position of a furnace tube in a semiconductor processing furnace is provided.
In a preferred embodiment, an apparatus for fixing the position of a furnace tube in a semiconductor processing furnace wherein the furnace is of the type that has a cylindrical body with an open end through which the tube may be withdrawn, a base on the open end, and wherein the tube includes a flange secured to the base through which gas may be withdrawn from or introduced into the tube, the tube is coaxially disposed within the furnace body, the apparatus may include two clamp halves each in a half-circular shape for engaging the flange on the tube onto the base; and means for mounting the two clamp halves to the base.
In the apparatus for fixing the position of a furnace tube in a semiconductor processing furnace, the base may be a manifold for withdrawing air from the tube. The two clamp halves may further include an internal cooling means, or an internal cooling that circulate a cooling medium therethrough, or an internal cooling means that circulates a cooling water therethrough. The apparatus may further include a Teflon spacer situated in-between the two clamp halves and the flange of the furnace tube. The furnace tube may be fabricated of quartz. The mounting means may include at least four bolts, or may include six bolts. The two clamp halves each may have a tongue section or a groove section for engaging an opposite clamp half that has a groove section or a tongue section. The two clamp halves may be joined at one end in a clam-shell configuration.
The present invention is further directed to a vertical furnace that is equipped with a quartz furnace tube for processing semiconductor wafers that includes a cylindrical-shaped quartz tube that has a sealed top and an open bottom, the open bottom may be provided with a flange portion; an annular-shaped base through which gas may be withdrawn from or introduced into the tube, the base may have a top surface for sealingly engaging the flange portion of the tube; and two clamp halves situated on top of the flange portion for mounting the tube to the base by mounting means.
The mounting means may include at least four bolts, or may include six bolts. The annular-shaped base may be a manifold that includes at least one gas outlet and at least one gas inlet. The two clamp halves may be connected by a hinge at one end such that the two halves operate in a clam-shell manner. The two clamp halves may further include internal cooling means, or may further include internal cooling means that circulates a cooling medium therethrough. The vertical furnace may further include a Teflon spacer positioned in-between the two clamp halves and the flange of the quartz tube. The two clamp halves may each be provided with a tongue and groove end.